1. Field of the Invention
The present invention relates in general to a device for sensing the displacement of working members in industrial equipment and, more particularly, to sensors for sensing the working member's angular displacement so as to control the motions of working members (boom, arm, bucket and the like) in industrial equipment such as power excavators.
2. Description of the Prior Art
As well known to those skilled in the art, various types of industrial equipment have been preferably used in construction sites and manufacturing plants for performing difficult operations which are beyond the power of man. Furthermore, not only are the buildings to be constructed and manufacturing lines of the plants run on very extensive scales, they have also been subdivided into many sections recently. Therefore, industrial equipment has been substituted for manpower while conducting difficult operations in the above construction sites and manufacturing plants.
Typical industrial equipment has a travelling part similar to that of a conventional vehicle. The travelling part moves the equipment to the desired place in the construction sites or manufacturing plants. Industrial equipment of this type also includes a plurality of working members for conducting several operations for digging sand and pebbles, digging ditches, loading goods and destroying buildings.
In the above industrial equipment, it needs to operate the working members carefully while conducting delicate operations. If an operator makes a mistake while operating the working members during a specific operation., safety accidents may occur. Power excavators are representative industrial equipment preferably used for digging. Power excavators have to be carefully controlled to accurately conduct the desired operations. In order to control the power excavators carefully, the angular displacements of the working members such as the booms, arms and buckets must be carefully controlled.
FIG. 1 is a view showing the construction of a typical power excavator. FIG. 2 is a partially enlarged perspective view of a joint portion between the boom and arm of the power excavator. The above power excavator is provided with a typical device for sensing the angular displacements of the working members.
As shown in FIG. 1, the power excavator 1 includes a turret 2 which is rotatably mounted to the top of a travelling part 3. The turret 2 forms the outer appearance of the excavator's top portion and has a control cap. The control cap is equipped with a control panel, a plurality of control levers and the like. The control levers are handled by an operator while operating the working members to conduct the desired operations. The travelling part 3 of the excavator 1 may be prodded with either wheels or caterpillars and moves the excavator to the desired place in accordance with the handling motions of the associated control levers of the control cap. The power excavator also includes a working member part 4 movably mounted to the front of the turret 2. The above working member part 4 includes a plurality of working members and directly conducts the desired operations in accordance with the handling motions of the associated control levers of the control cap.
The working members of the above part 4 include a boom 5, an arm 6 and a bucket 7 which move within their own moving ranges. The joint portions between the working members 5, 6 and 7 are each provided with a displacement sensing device 8. The sensing devices 8 of the power excavator sense the working member's angular displacements and control the motions of the working members while performing the desired operations.
FIG. 2 shows the sensing device 8 which is provided in the joint portion between the boom 5 and the arm 6 and is used for sensing the angular displacement of the arm 6 relative to the boom 5. The above sensing device 8 includes a sensor housing 9 having a predetermined configuration. The above housing 9 is mounted to the boom 5 at the joint portion between the boom 5 and the arm 6. A sensor (not shown) is received in the housing 9 and senses the angular displacement of the arm 6 relative to the boom 5. A bracket 10 is mounted to the arm 6 outside the housing 10 at the joint portion. The bracket 10 is also connected to the above housing 9.
Generally, the sensor provided in the housing 9 may use a potentiometer. When the working members of the above excavator 1 are operated to conduct the desired operation, the arm 6 will perform the arm-in or arm-out motion relative to the boom 5. The turning motion of the arm 6 rotates the housing 9 connected to the bracket 10, thereby varying the variable resistance of the sensor. The sensor thus detects the angular displacement of the arm 6 relative to the boom 5 by checking the variation of the constant voltage applied from a battery to the sensor.
As the above sensing device detects the angular displacements of the working members in accordance with constant voltage variation as described above, the device is largely influenced by moisture thereby often failing to precisely detect the angular displacements of the working members. In order to rectify the above problem, expensive waterproof sensors may be used. However, the waterproof sensors increase the cost of the displacement sensing device.
The above expensive sensor needs to be protected by the housing 9. However, the above housing 9 makes it difficult to change the sensor with a new one. Furthermore, it is very difficult to precisely focus the sensor when initially installing the sensor in the housing 9.
In addition, the sensing device vibrates intensely as the sensing device is mounted to either side surface of the working member. As the vibrations cause operational errors to the sensing device while sensing the angular displacements of the working members, the sensing device fails to precisely sense the angular displacements of the working members.